1. Field of the Invention
The present invention relates to electromagnetic interference reducing apparatus and, more particularly, to an assembly for reducing the amount of electromagnetic interference escaping from an equipment enclosure out of which pass a plurality of electrical conductors.
2. Background Art
Many electronic systems are known which emit electromagnetic radiation in their operation. Such radiation is also known, depending on its nature, to affect other electronic systems. In order to control electromagnetic interference between electronic systems, the various government agencies have specified maximum levels of electromagnetic radiation emissions which may be allowed. These levels must be met for the equipment to be sold. An optimum method for restricting electromagnetic emissions is to totally enclose the electronic system in a shielded housing thereby restricting all emissions there from.
In the area of certain types of systems with widely separated elements such as telephone switching system, total sytem enclosure is not possible because subscriber related wiring must leave the system enclosure. In such conditions, allowable levels of emissions have been found obtainable by treating the individual wiring conductors to remove electromagnetic interference traveling on them before the conductors leave the enclosure. A common way to treat such conductors is to capacitively couple the individual conductors to the enclosure at the point they pass through a wall of the enclosure. In this regard, it is known to provide capacitive bypassing in the form of an array of feed through capacitors mounted in a conductive plane and having a first feed through terminal on a inner surface, a second feed through terminal on the outer surface and having a ground sleeve connected to the enclosure wall. A plurality of conductors passing out of the enclosure are first terminated to the inner feed through terminals. A corresponding plurality of second conductors are then connected to the outer feed through terminals and routed to the subscribers' telephone equipment. Such an arrangement, while operating generally satisfactorily, requires the individual manual connection of conductors on the feed through assembly mounted to the enclosure.
Another known method of treating conductors passing out of an enclosure to subscribers' telephone equipment is to mount a plurality of capacitors on a printed wiring board which is then mounted to an inner surface of a wall of the enclosure by means of screw fasteners. A first printed conductor on the board provides a circuit path to connect a first terminal of each of the capacitors to the enclosure wall and a plurality of second circuit conductors connect a second terminal of each of the capacitors to a corresponding first and second plated-through hole. The free ends of the conductors passing out of the enclosure and then soldered to a corresponding first plated-through hole. A second cable is provided and connected between the second plated-through hole and the equipment within the enclosure. Such an arrangement while operating generally satisfactorily requires the separate assembly of capacitors and printed wiring card to the enclosure and the assembly of the cables to the printed wiring card mounted within the enclosure.
The above arrangements have generally been found to be bulky, expensive and costly to install, and in the case of the printed wiring card of reduced effectiveness due the placement of treating capacitors at a less than ideal position for effective electromagnetic interference reduction.